In the medical field, it is frequently required to establish a connection between blood vessels (veins and arteries) and injectors or containers of different kinds. The connection must be made with total sterility. Leakage must be avoided as far as possible. Examples of treatments requiring blood vessel contact are blood transfusion inclusive blood giving, blood sampling with the assistance of test containers under negative pressure, and intravenous supply of medicine, nourishment or just liquid for blood volume expansion, commonly called a drip. In all these applications it is essential that the puncture of the vessel wall can be done without damage to the surrounding tissues. Failures are unpleasant, even under the best circumstances, but may cause serious damage as well.
A common syringe for insertion in blood vessels of different kinds is shown in FIG. 1. The syringe consists of a tube body (1) with a channel that continues in a thin plastic tube (3). The rear opening of the tube body is designed with a conical widening for attachment to a syringe or a catheter. The opening is at the beginning filled by the hollow needle (4), which continues with the needle body (5), the rear part of which has a transparent room, which gets filled with blood, when satisfactory blood vessel contact has been established. Through the channel runs the hollow puncture needle (4) with a beveled, sharpened tip, which extends a few millimeters in front of the front end of the thin plastic tube.
When establishing a blood vessel connection, one chooses a suitable, superficial blood vessel (vein or artery, depending upon type of treatment) and tries to direct the tip of the puncture needle to penetrate the skin just over the chosen blood vessel so that the tip hits the vessel centrally. After penetration of the vessel wall the puncture needle with the plastic tube can be directed axially obliquely into the blood path. When the above mentioned transparent room behind the needle starts filling with blood the needle body with the belonging puncture needle is kept still, while the tube is advanced so that the needle tip no longer is in front of the end of the plastic tube. This is done to prevent the needle tip from hurting the vessel wall, when the plastic tube afterwards is brought forward into the blood path, to the main part of its length, with the aid of the tube body. When the plastic tube has reached the desired position in the blood path, the tube body is kept still. The puncture needle, which, so far, has prevented leakage by its close fit to the inner wall of the plastic tube, is withdrawn with the needle body and the desired connection to the syringe, container or catheter is made.
For reasons of sterility the plastic tube must not be touched before or during the insertion into the blood lumen. The distance from the needle tip to the grip around the needle body is long. The grip surfaces are not well defined, especially as the hands most frequently have to be provided with gloves. The insertion demands a number of complicated changes of direction. After the skin penetration there is no visible indication of the position of the needle tip. Moreover, the blood vessels are frequently badly fixed under the skin and have troublesome tendencies to "roll away".
In spite of these, from the ergonomic point of view, very unfavorable circumstances, experienced nurses with daily training become very skilled and seldom fail. The circumstances are different for doctors, nurses, ambulance crews and apprentices, who are infrequently put to the task. Failures will cause the patient discomfort and are embarrassing to the operator. Further, loss of valuable material will arise.
Amendment proposals concerning the ergonomics at the establishment of vein and artery connections and similar operations can be found in the German "Offenlegungsschriften" 2306068 and 4244563. The solution of the problem according to the former is applicable to injection needles without a surrounding plastic tube only. While it is true that the latter reference mentions the possibility of combination with a plastic tube, the proposed design causes large risks of damages as no firm connection between the needle body and the tube body exists. As will be explained below unintended displacements between those parts cause serious moments of risk.